1. Field of the Invention
The present invention relates generally to semiconductor technology, and more particularly to a through-silicon via (TSV) for connection of stacked chips and a method for forming the same.
2. Description of the Prior Art
Through-silicon via is typically fabricated to provide the through-via filled with a conducting material that passes completely through the silicon substrate layer to contact and connect with the other TSVs and conductors of the bonded layers. For example, a vertical hole is defined through a predetermined portion of each chip at a wafer level. An insulation layer is formed on the surface of the vertical hole. With a seed metal layer formed on the insulation layer, a metal is filled into the vertical hole through an electroplating process to form a TSV. Then, the TSV is exposed through back-grinding of the backside of a wafer.
After the wafer is sawed and is separated into individual chips, at least two chips can be vertically stacked, one atop the other, on one of the substrates using one or more of the TSV. Thereupon, the upper surface of the substrate including the stacked chips is molded, and solder balls are mounted on the lower surface of the substrate.
Typically, to form a TSV, a continuous copper seed layer is employed inside a recessed via feature. For example, U.S. Pat. Pub. No. 2009/0226611 A1 discloses that to form a void-free bulk copper metal filling of a recessed feature in integrated circuits, the interior sidewalls of the recessed feature is covered with a continuous, smooth copper seed layer.
U.S. Pat. Pub. No. 2010/0200412 A1 teaches that it is undesirable to form a seed layer that is significantly thicker around the TSV opening because the thick seed layer around the TSV opening results in lower resistance at the opening and consequently high local deposition rates.
As the dimension of the TSVs shrinks, it becomes more and more difficult to form a void-free or seamless copper plated TSV structure. Therefore, there is a need in this industry to provide an improved method in order to form a void-free or seamless copper plated TSV structure.